just this year I talked to an instructor who had that exact same problem happen to him with gorilla's. He was on a dive and first one blade came off, then right before he was able to get back into the boat the other blade came off. Weird.
this is only the second time I have ever heard of this happening, so I don't think its that common, of course we are talking about 16 year old fins here. I love mine, and hope they last for another 16 years, but I keep looking for a new pair of fins that will compare to these. I still think the gorillas were the best fins made. hmm think I will hit ebay and try to find another pair so I have some extra.